P0571 Type Requirements for <numeric> Algorithms

[wg21bot]

P0571R2 Type Requirements for <numeric> Algorithms (Bryce Adelstein Lelbach)

[mclow]

This has old-style wording; I have informed Bryce that a revision is needed

[ogiroux]

I don't think SG1 needs to see this again.

[mclow]

This was not adopted for C++20. Removing the "C++20" label.